1. Field of the Invention
The present invention relates to a secondary battery, and, more particularly, to a secondary battery including a cap assembly with a tighter binding structure that binds an electrode port and a cap plate, and a method of manufacturing the cap assembly.
2. Description of the Related Art
Secondary batteries, which are distinguished from primary batteries due to their ability to be repeatedly charged and discharged, have been widely used in cellular phones, notebook computers, camcorders, and other portable electronic devices. Lithium secondary batteries having an operating voltage of 3.6V or greater, which is three times higher than nickel-cadmium (Ni—Cd) batteries, popularized as a power source for various kinds of electronic equipment, and nickel-hydrogen batteries, are nowadays frequently used because of their high energy density per unit of weight.
Such lithium secondary batteries mostly use lithium oxide as a negative active material, and a carbonaceous material as a positive active material. Lithium secondary batteries can be classified into liquid electrolyte batteries, also known as lithium ion batteries, and polymer electrolyte batteries, also known as lithium polymer batteries, according to the type of electrolyte used. Lithium secondary batteries are manufactured in various shapes, typically in cylindrical, rectangular, or pouch forms. An example of a rectangular secondary battery with a cap assembly is disclosed in U.S. Pat. No. 6,509,115.
FIG. 1 is an exploded perspective view of a conventional cap assembly for a rectangular secondary battery. As shown in FIG. 1, a cap assembly 10 includes a cap plate 11 covering a top opening of a can, which accommodates a battery unit, an electrode port 12 coupled to the cap plate 11 via a gasket 13 acting as an insulator, and an insulating plate 14 placed underneath the cap plate 11. The electrode port 12 coupled to the cap plate 11 is electrically connected to a negative tab or a positive tab drawn out from the battery unit to act as a negative port or a positive port.
FIG. 2 is a sectional view of the assembled cap assembly of FIG. 1. As shown in FIG. 2, the electrode port 12 is inserted into a port aperture 11a (see FIG. 1) of the cap plate 11. The cap plate 11 and the electrode port 12 are insulated from one another via the gasket 13. The insulating plate 14 is positioned underneath the cap plate 11 to insulate an end of the electrode port 12, protruding out of the port aperture 11a of the cap plate 11, from the cap plate 11. The protruding end of the electrode port 12 is stretched out, via spinning, to support the insulating plate 14 upward, as illustrated in FIG. 2. Accordingly, the electrode port 12 is fixed to the cap plate 11 and the insulating plate 14.
In the cap assembly 13 having the above-described structure, since the electrode port 12 is slid into the gasket 13, the electrode port 12 is movable with respect to the gasket 13 by external impacts. Accordingly, the negative tab or positive tab that supports the end of the electrode port 12 is also movable, increasing the possibility of a short circuit due to a contact between the electrode tab and the inner wall of the can.
In addition, it is highly likely that an electrolyte injected into the can will leak through a gap between the electrode port 12 and the gasket 13. Furthermore, since the gasket 13 and the insulating plate 14 are designed as separate parts, the cap assembly is assembled from more parts and the assembling process is complicated.